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Heat conductivity depending on temperature

  1. Apr 7, 2009 #1
    Hi, I'm working on my final year project for a part time mechanical engineering design degree course. I've built and tested a heat exchanger which is used for controlling the temperature of N2 gas.

    I'm currently working through the calculations so I can compare real against calculated values.

    I'm struggling to calculate the thermal conductivity of N2 depending on temperature. An Engineer from work gave me a Visual basic file which had the following expression which works really well. The problem is I can't work out what the components are - and I'm not happy using it if I don't understand what it's doing


    Visual basic expression.

    Function lambda_N2 (Temp As Double)

    ' Calculation of heat conductivity (W/(m*K)) depending on temperature
    ' for gaseous N2 - source Malkov

    lambda_N2 = 0
    lambda_N2 = -0.000000054111 * Temp * Temp + 0.000102445 * Temp - 0.00016339

    End Function

    I assume that the values he's used are constants - but as yet I've been unable to trace them. Could someone explain what some or all of it is doing?

    Or is there another way of calculating thermal conductivity?
    (Note. I want it for an individual temperature not for ∆T)

    Many thanks in advance
    Oli
     
  2. jcsd
  3. Apr 7, 2009 #2

    Mapes

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    Gold Member

    Hi Oli, welcome to PF.

    The equation looks like an empirical fit to experimentally measured results (and as such, has little meaning without a temperature and pressure range). The constants are likely selected just to make the resulting curve fit well to measured values.

    A much more involved equation with physical justification is given http://www.boulder.nist.gov/div838/theory/refprop/NAO.PDF" [Broken], which may be what you're looking for. The document also includes many references to experimental work, which may be useful.
     
    Last edited by a moderator: May 4, 2017
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